The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system adopting a Wideband Code Division Multiple Access (WCDMA) air interface technique, and the UMTS adopts a structure similar to that of the second generation mobile communication system, including a Radio Access Network (RAN), a Core Network (CN), and User Equipment (UE). The RAN is configured to process all functions associated with wireless communication. The CN is configured to process all speech calling and data connection functions in the UMTS, and perform switching and routing functions with external networks. The RAN in the UMTS system is a UMTS Territorial Radio Access Network (UTRAN).
FIG. 1 is a schematic structural view of a UMTS. The UTRAN includes one and more Radio Network Subsystems (RNSs), in which each RNS is formed by one Radio Network Controller (RNC) and one or more NodeBs. Each RNC is connected with the CN via an Iu interface, each NodeB is connected with the RNC via an Iub interface, and the RNCs are interconnected with each other via an Iur interface. Each RNC is configured to allocate and control wireless resources of the NodeBs connected with the RNC or associated with the RNC, and each NodeB is configured to perform a data stream conversion between the Iub interface and a Uu interface, and meanwhile is participated in part of the wireless resource management.
The network architecture shown in FIG. 1 is based on the architecture of a version earlier than 3GPP Release 6. Considering the competition capability of the network in the future, the 3GPP has been researching on a brand new evolved network architecture to satisfy the application requirements of a mobile network in the future, which includes a system architecture evolvement (SAE) and a long time evolvement (LTE) of the access network, and the network evolvement aims at providing a totally IP-based network with a low delay, high data rate, high system capacity and coverage, and low cost.
FIG. 2 is a schematic architectural view of an evolved network. The network architecture includes a UE, an Evolved UMTS Territorial Radio Access Network (E-UTRAN), and an Evolved Packet Core (EPC). The E-UTRAN is formed by eNodeBs, in which the eNodeBs are connected with each other via an X2 interface. The EPC includes a Mobility Management Entity (MME), a serving SAE gateway, and a Packet Date Network SAE gateway (PDN SAE gateway). The MME is responsible for the mobility management of a control plane, including managing user context and mobility status, assigning a user temporal identifier (ID), and the like. The MME is connected with a Serving GPRS Support Node (SGSN) in an existing network via an S3 interface, connected with the E-UTRAN via an S1-MME interface, and with the Serving SAE Gateway via an S1-U interface. The MME is configured with a timer therein. The Serving SAE Gateway is responsible for initiating a paging for a downlink data in Idle state, managing and saving IP bearer parameters and routing information in a network, and the like. The PDN SAE gateway serves as a user plane anchor point among different access systems. The system shown in FIG. 2 further includes a Policy and Charging Rule Function (PCRF) and a Home Subscriber Server (HSS).
In the evolved network architecture, a handover of X2 interfaces exists between the eNodeBs. If an eNodeB where the UE is currently located is called a Source eNodeB (S-eNB), and an eNodeB where the UE will be handed over to is called a Target eNodeB (T-eNB), the above handover refers a process that the UE is handed over from the S-eNB to a cell controlled by the T-eNB.
In actual applications, the EPC needs to send an NAS message to the UE through the eNodeB to realize a service corresponding to the UE, in which the time point and time interval for sending the NAS message vary with different services. In the conventional art, there is a solution for NAS message processing if the handover is successful. Unfortunately, if the handover fails, no technical solution is available for enabling the EPC to send the NAS message to the UE.
Therefore, in the solution for NAS message processing in the conventional art, the EPC cannot be informed timely if the handover fails, that is, the UE returns to an S-eNB service area again, and as a result, the EPC cannot correctly send the NAS message to the UE.